3000/m on 500/y is extremely inexpensive. They will not find cheaper for 4 people without driving up transportation costs and killing leisure time. They probably have an affordable car, as compacts tend not to be "luxury" cars with many bells and whistles to maintain. Tuition, well, you pay for what's important to you, and obviously they would rather dump this into the kids than saving. Hardly worth criticizing as excess. Groceries and eating out are not going to get cheaper. They are already less than $10 per day per person. Again, one couldn't call that excessive.

$3000 monthly is less than 10% of the household income so I don't see how that could ever be considered frivolous.

Public schools are no good in SV, so either I have to spend $4500 as rent in a good school district or spend low in rent and send kids to private school. And $3000 is the cheapest you can get in a decent location in SV

You can go to a public school but if you want it to be a quality one your rent of a house will not be a 3k.